The crusader kingdom of Jerusalem was born at the very end of the eleventh century. On 15 June 1099, around noon, the crusaders poured over the battered walls of Jerusalem. They had been fighting for two nights and a day; they had walked for three years from Europe; they had endured sieges, battles, and starvation; they were tired, they were angry, and they wanted revenge.
For three days the crusaders slaughtered all the Muslims and Jews in Jerusalem. The chronicles are blunt: eyewitness Raymond of Aguilers described visiting the Temple Mount where he had to ‘pick his way through corpses and blood that reached up to his knees.’
Muslims were shocked. Previously they had been happy to form alliances with the Christian crusaders since the Muslim world’s alliances were much fragmented but this was a lesson in brutality which was never forgotten. At the least, the Muslims determined to expel the crusaders who now held large swathes of territory from North Syria to Southern Israel.
Acre: The Templars' Last Battle, Michael Baigent in http://www.freemasonrytoday.com/41/p11.php